In prior art, a wrapping machine used to wrap a plastic foil web around an object to be wrapped is known. Similarly, a top foil wrapping machine used to set a desired length of top foil onto an object to be wrapped is known.
The object to be wrapped is usually a load placed on a pallet, which typically is an assembly of the form of a rectangular parallelepiped. A feature common to the wrapping machine and the top foil wrapping machine is that they comprise a machine frame supported on a fixed floor base. The frame usually comprises four upright vertical columns. The wrapping machine or top foil wrapping machine further comprises a lifting frame arranged to be vertically movable upwards and downwards, being guided by the vertical columns. Further, the wrapping machine or top foil wrapping machine comprises a lifting motor for moving the lifting frame, and power transmission means for the transmission of power from the lifting motor to produce vertical motion of the lifting frame. The power transmission means comprise elongate flexible drive elements and wheels for the transmission of the power of the lifting motor to the drive elements.
The wrapping machine further comprises a foil dispenser, on which a foil web roll can be rotatably supported. Supported by the lifting frame is a wrapping frame, which usually forms a circular endless path for the foil dispenser. The foil dispenser circulates along this path around the object to be packaged, allowing the plastic foil web to be unrolled from the foil web roll to form a wrapping around the object to be packaged.
The top foil wrapping machine has a top foil depositor supported on or connected to the lifting frame and arranged to deposit a top foil from the top foil web roll onto the object to be wrapped.
This type of prior-art wrapping machine or top foil wrapping machine has a so-called top frame fixed to the upper ends of the vertical columns and consisting of beams connecting the upper ends of the vertical columns. The lifting motor is connected to this top frame. The aforesaid elongate drive elements of the power transmission means transmitting the power of the lifting motor to produce a vertical motion of the lifting frame are power transmission chains and the wheels are chain sprockets. Mounted at the upper and lower ends of each vertical column are diverting sprockets, over which the vertically moving endless chain runs. The lifting frame is fixed to these vertical chains. A diverting sprocket on one of the vertical columns is driven by the lifting motor. From this single lifting motor, power is correspondingly transmitted to the other side of the machine by chains via diverting and tensioning sprockets rotatably mounted on the top frame. The diverting sprockets at the upper ends of opposite vertical columns are connected to each other by shafts. With this arrangement, the lifting frame fixed to the chains at four points is raised and lowered evenly by means of a single lifting motor.
A problem with the prior-art wrapping machine or top foil wrapping machine is that the task of assembling it is difficult to carry out. Numerous parts have to be mounted on the top frame at a relatively large height from the floor level, which, besides being difficult, is also problematic in respect of work safety. The prior-art wrapping machine or top foil wrapping machine contains various parts requiring regular maintenance that are located at a large height. For example, the bearings of the shafts and sprockets have to be repeatedly lubricated, which is why it is necessary to provide special lubricant pipes for passing a lubricant to the objects to be lubricated. Further, the mechanism needed for moving the lifting frame in the prior-art wrapping machine or top foil wrapping machine comprises a very large number of components, resulting in a complicated and expensive construction. Moreover, as the lifting motor, which usually is an electric motor, is mounted on the top frame, very long cables are needed for electricity supply and control.